This invention is directed to a process of melt spinning eccentric bicomponent filaments.
Eccentric bicomponent filaments have the property of self-crimpability, by virtue of the differential between the shrinkage of the two components of the filament. This property is useful in textiles for making stretch fabrics such as hosiery. Preferably, one component is eccentrically disposed entirely within the other component, whereby the first-mentioned component is the core component and the other component is the sheath component, such a shown in FIG. 5 of U.S. Pat. No. 3,244,785. This surrounds the lower melting core component with the higher melting sheath component to prevent the filaments from sticking together when converged after melt spinning. Because of the eccentric disposition of the core within the sheath, the sheath has a cross section that varies from a thin region to a thick region relative to one another.
U.S. Pat. No. 3,244,785 discloses a process for making an eccentric sheath-core filament by first forming a concentric arrangement of a core of one molten polymeric component in a sheath of another molten polymeric component, and while this concentric arrangement is still in molten form, injecting additional molten sheath polymeric component along one side of the concentric arrangement to force the core polymeric component to an eccentric position within the sheath. A row of the eccentric bicomponent filaments is melt spun and gas quenched during convergence (bringing together) of the filaments into yarn, and then the yarn is wound into a package. Between convergence and windup, the filaments can be treated, such as with steam, for dimensional stabilization. The yarn is then cold drawn at least about 4X and then heated at as low tension as possible to precrimp the yarn, followed by stretching to temporarily suppress the crimp and then making a fabric out of the yarn. In the case of the special filament compositions disclosed in Segraves and Mulholland, U.S. Pat. application Ser. No. 581,158, filed May 27, 1975 (Belgian Pat. No. 831,930), the cold drawn yarn can be made into the fabric directly, i.e., without precrimping, and then the fabric can be heated to develop the crimp for the first time.
U.S. Pat. No. 3,535,844 discloses a spinneret assembly for melt spinning a pair of rows of the sheath-core eccentric filaments of the type disclosed in U.S. Pat. No. 3,244,785, to thereby increase melt spinning capacity without undesirable crowding of the filaments and without increasing spinneret size. This is done by alternating the direction of the passages for injecting the sheath polymer along the side of the concentric sheath-core arrangement. The resultant filaments are spun with the thin sheath regions oriented to face the quench gas flow in one row and to face the opposite direction in the other row.
U.S. Pat. No. 3,704,971 discloses a spinneret assembly which doubles the production capacity of the spinneret assembly of U.S. Pat. No. 3,535,844 by providing a second pair of rows of orifices for melt spinning the filaments, with the orientation of the thin sheath regions of the filaments in this second pair of rows being a repetition of the opposite facing arrangement of U.S. Pat. No. 3,535,844 in the first pair of rows. In the embodiment shown in the patent, the distance between the pairs of rows is greater than the distance between the rows in each pair.
The spinneret assembly of U.S. Pat. No. 3,704,971 has operated satisfactorily to produce 18 denier yarn composed of eight eccentric sheath-core filaments (5.85 dpf as spun) converged together in a single step from two orifices in each of the four rows of orifices. When the spinneret assembly was used to make 17-3 yarn (22.3 dpf as spun), by grouping two adjacent filaments from one row with another filament from the adjacent row of the same pair of rows, the filaments randomly stuck to one another in the yarn converged therefrom. These stuck together portions would not crimp adequately, and the resultant poorly crimped portions caused appearance defects in fabric made therefrom. This sticking problem was unpredictable in the sense that sometimes it occurred under a given set of operating conditions, e.g., melt (spinning) temperature, windup rate, quench air temperature and velocity, and convergence guide friction, all of which affect the condition of the filament at convergence into a bundle, and sometimes the sticking did not occur. Summary of the Present Invention
The present invention involves the discovery that this sticking of filaments together occurs only when the thin sheath region of one filament comes into contact with the thin sheath region of another filament during convergence, despite the fact that the entire outer surface of each filament is of the same sheath polymer. This sticking occurs under the same operating conditions as when sticking does not occur upon contact between the thin sheath region of one filament with the thick sheath region of another filament or between two thick sheath regions. Consequently, the present invention involves the selection of filaments from an array of melt spun filaments for convergence into bundles in which contact betwen thin sheath regions during convergence does not occur.
More specifically, the process of the present invention arises in the process of melt spinning a plurality of filaments each having a core component eccentrically disposed within a sheath component, the eccentricity of the core component within the sheath component providing the sheath component with a cross section varying from a thin region to a thick region relative to one another, gas quenching said filaments and converging said filaments together into yarn, wherein the converged together filaments randomly stick together, the improvement comprising selecting the filaments to be converged into said yarn to avoid contact between the thin sheath regions of the filaments during convergence, the number of filaments required for said yarn being at least three and requiring the convergence into at least one bundle to avoid said contact, said one bundle being said yarn when the number of filaments therein is equal to the number required for said yarn, and when more than one bundle is formed by said convergence to obtain avoidance of said contact, converging the resultant bundles together into said yarn, whereby the thin sheath regions of the filaments in said yarn do not stick together.
The selection of the filaments and the number of bundles formed from the filaments for subsequent convergence into the yarn will depend on the number of filaments required for the yarn and on the thin sheath orientation of the filaments in the array of filaments being melt spun. For example, with proper selection of filaments from the array, a three filament yarn will require only one convergence step into the yarn. On the other hand, a seven filament yarn will require convergence first into bundles of the desired number of filaments in each, wherein thin-sheath to thin-sheath contact during convergence is avoided, followed by convergence of the bundles into the yarn. The solution to the problem provided by the present invention does not involve expensive reconstruction of equipment such as the quench chimney and does not require any sacrifice in production capacity. This solution also eliminates the sensitivity of filament-to-filament sticking to slight and sometimes undetected changes in the above described operating conditions. The sticking of melt spun filaments together is in essence a condition of overcrowding. The present invention alleviates this overcrowding without requiring an increase in spinneret size.